The state-of-art screw feed-in devices currently available in the market generally comprise a handle and driving head. Within the driving head, a guiding channel is provided for escorting the strip on which the screws are equally spaced. Above the guiding channel, a toothed wheel is mounted in such a manner that when the toothed wheel is rotated an angle equal to the pitch thereof, the screw strip will advance a distance equal the spacing between two adjacent screws.
According to the conventional screw feed-in devices, the feed-in toothed wheel is controlled by a post which is received within an arcuated slot and in mechanical engagement with the handle so that when the handle is lowered down, a clutch member mounted on the post engages the counterpart member secured to the toothed wheel and thus causing an angular movement of the toothed wheel as the post is moved within the arcuated slot. In this way, the screw strip is advanced when the handle is operated.
Theoretically, each lowering-down of the handle will advance the screw strip a distance exactly equal to the spacing between two adjacent screws on the strip and one of the screws should be exactly placed at a location where a screw driver can reach to carry out the screw tightening operation.
One of the disadvantages of the conventional screw feed-in apparatus is the complexity in structure of the clutch members used to mechanically connect the post and the toothed wheel. This not only increases the manufacturing cost of the screw feed-in device, but also requires a more sophisticated technique in manufacturing.
Further, in the conventional screw feed-in device, the advance of the screw strip is done by the lowering-down of the handle. Once the handle is not lowered a suitable distance, the strip will not be moved to exactly have the next screw be placed at the position where the screw driver can normally reach and this results in a difficult situation for the screw driver to correctly engage and tighten the screw. Usually, a manual correction is required to move the screw to be in alignment with the screw driver.
It is therefore desirable to provide an automatic screw feed-in apparatus which comprises an automatic screw advancing mechanism to overcome the above-mentioned problems.